Salt stress affects sterol biosynthesis in the halophilic black yeast Hortaea werneckii

Hortaea werneckii is a black yeast recently isolated from salterns in Slove nia. Some of the adaptations of halophilic microorganisms to increased sali nity and osmolarity of the environment are alterations in membrane properti es. By modulating the fluidity, sterols play an important role as a compone nt of eukaryotic biological membranes. We studied the regulation of sterol biosynthesis in H. werneckii through the activity and amount of 3-hydroxy-3 -methylglutaryl coenzyme A reductase (HMG R), a key regulatory enzyme in th e biosynthesis of sterols. We found some differences in the characteristics of HMG R and in its regulation by different environmental salinities in H. werneckii when compared to the mesophilic baker's yeast, Saccharomyces cer evisiae. Our results suggest that halophilic black yeast regulates sterol b iosynthesis through HMG R in a different way than mesophiles, which might b e a consequence of the different ecophysiology of halophilic black yeasts. From this perspective, H. werneckii is an interesting novel model organism for studies on salt stress-responsive proteins as well as on sterol biosynt hesis in eukaryotes. (C) 1999 Federation of European Microbiological Societ ies. Published by Elsevier Science B.V. All rights reserved.